Micro-EDXRF investigation of Chalcolithic gold ornaments from Portuguese Estremadura

Valerio, P.; Soares, A. M. M.; Araujo, M. F.; Carvalho, A. F.

Key information

Authors:

Valerio, P. (Pedro Manuel Francisco Valério); Soares, A. M. M. (António Manuel Monge Soares); Araujo, M. F. (Maria de Fátima Duarte de Araújo); Carvalho, A. F.

Published in

03/20/2017

Abstract

Chalcolithic gold artefacts assigned to the Bell Beaker Culture in Portuguese Estremadura were analysed by micro-energy dispersive X-ray fluorescence spectrometry. These high-status jewels comprise beads of tubular, spiral and double-conical type, a spiral ring and a wire fragment. The collection is mainly composed of gold with 8.7–16.3 wt% Ag and <0.04 wt% Cu. Additionally, there is a typologically uncommon double-conical bead showing a lower Ag content (6.7 wt%). The relative intensity of the Ag-Kα and Ag-Lα X-rays from artefacts established the existence of a surface layer depleted in silver, while the reasonable effective penetration depth of the Ag-Kα (about 25–30 μm) provided suitable results for such high fineness gold alloys. A uniform Au–Ag composition at the joint indicates that the double-conical bead was made by joining two sheets without solder. Overall, the collection shows a composition that is similar to known Chalcolithic gold in Portuguese Estremadura but different from coeval gold in Southwestern Iberian Peninsula. The distinct compositional pattern of Chalcolithic gold in Portuguese Estremadura seems to be inconsistent with the natural variability of silver content in alluvial deposits of gold in Iberian Peninsula, thus suggesting a continuous use of particular sources and limited exchange of nuggets and jewels with the neighbouring region.